Provide a "controlled" searchable dropdown

[ScopeyNZ]

Right now, the search functionality in dropdowns is "uncontrolled" meaning that an implementation needs to handle the event of the user typing in the search box, and narrow down the options themselves. This is useful when you want to do some custom search behaviour (like loading from an API), but is a little verbose for the commonly used search functionality.

While it can be trivial to get the search working, it can be more nuanced to solve problems like filtering out already selected items when searching for others.

Ideally theres a SearchDropdown component or something that just implements a common text search on the existing items in the dropdown, and can handle the gotcha of retaining already selected items in search results.